Reversal of the lift force on an oblate bubble in a weakly viscous linear shear flow

• Published in: Journal of fluid mechanics Vol. 628; pp. 23 - 41
• Main Authors: ADOUA, RICHARD, LEGENDRE, DOMINIQUE, MAGNAUDET, JACQUES
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.06.2009; Cambridge University Press (CUP)
• Subjects: Drops and bubbles; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Fundamental areas of phenomenology (including applications); Hydrodynamic stability; Instability of shear flows; Mechanics; Nonhomogeneous flows; Physics; Upstream; Oblate spheroid; Bubbles; Shear flow; Digital simulation; Hydrodynamic instability; Vorticity; Modelling; Lift coefficient; Viscous fluids; Drag coefficient; Oblate bubble; Fluid Mechanics; Weakly viscous flow
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/S0022112009006090

We compute the flow about an oblate spheroidal bubble of prescribed shape set fixed in a viscous linear shear flow in the range of moderate to high Reynolds numbers. In contrast to predictions based on inviscid theory, the numerical results reveal that for weak enough shear rates, the lift force and torque change sign in an intermediate range of Reynolds numbers when the bubble oblateness exceeds a critical value that depends on the relative shear rate. This effect is found to be due to the vorticity generated at the bubble surface which, combined with the velocity gradient associated with the upstream shear, results in a system of two counter-rotating streamwise vortices whose sign is opposite to that induced by the classical inviscid tilting of the upstream vorticity around the bubble. We show that this lift reversal mechanism is closely related to the wake instability mechanism experienced by a spheroidal bubble rising in a stagnant liquid.